Eccentric gear pump



prl 29, 194i. M. SCHMITZ ECCENTRIC GEAR IUMP Filed Feb. 28, 1940 2 Sheets-Sheet l INVENTOR. /baf/ Z'/W//z ATTORNEY.

www

M. sci-:MITI

EccENTmo GEAR PUMP Filed Feb. 28, 1940 2 Sheets-Sheet 2' @7W 9 MW I W Q y ATTQRNEY.

e at or near the points of contact.

Patented Apr. v29, 19,41

UNITED` STATES PATENT OFFICE ECCENTRIC GEAR PUMP Michael Schmitz, Ferndale, Mich.

Application February 28, 1940, Serial No. 321,228

A(CI. S- 126) 2 Claims.

The following is a continuation-impart of my copending application, Serial No. 227,538, filed August 30, 1938.

The present invention pertains to a novel pump of the internal eccentric gear type.

In order to obtain an accurate running seal in pumps of this character, it is essential to machine the ygears Very accurately, and in fact complicated gear :formulas have been proposed for this purpose. The accuracy of the gears is however destroyed after a comparatively short period of service because of abrasives in` the fluid in addition to normal wear.

The principal objects of the invention are, first, to obtain a running seal without complicated gear machining and, second, to maintain the seal notwithstanding the passing of abrasives through the pump. These objects are accomplished generally by forming one of the gears, preferably the outer or driven gear, of a resilient compressible material and by causing the inner or driving gear to compress the resilient gear It is understood vin this connection that the gears are eccentric to eachother, and the center distance required for a normal running iit may be regarded as the theoretical center distance. This distance, according to a preferred form of the invention, is altered so that the gears would bind or jam if both were made of metal. Be-

cause of this alteration of the theoretical center distance, the resilient gear is compressed by the other gear during the operation of the pump. This compression occurs at sufficient points at least to maintain the intake chamber sealed from the outlet lchamber, and preferably at each tooth of the driving pinion in order to seal each of the pockets.

In pumps of this character it has been customary to admit the fluid at one end of the intake chamber. These pumps operate at high speed and at times'can carry more iiuid than 'can be supplied inthis manner.- Another object Vof the invention is to increase the fluid supply and is accomplished by dividing or branching the intake chamber so that it communicates with both ends of the internal gear. In order to accommodate the pump 'to this construction, the

housing thereof is preferably cast in two parts.

vAnother 'object of the invention is to improve t'he sealing of the pump housing. Ordinarily one end of the internal gear communicates with the intake and outlet chambers, and the other is often leakage in this area. This difculty is overcome in the present invention by providing a wall across this end of the gear and integral therewith so that the gear seals itself except at the end communicating with the intake and outlet chambers. Preferably the resilient material constituing this gear is 'impregnated with a lubricant to reduce the friction with the gear housing parts and the metal driving pinion. The closed internal gear may be used independently of the altered center distance described above.

Still another object of the invention is to provide a pump that can be supported entirely in the fluid line, that is, without a base structure. In this case the housngI is made substantially cylindrical, or at least balanced in weight, with the intake and outlet chambers adapted to be coupled in the line. The entire pump, if not too large, can be supported solely by the pipe line.

The invention is fully disclosed by way of example in the following description and in the accompanying drawings in which:

vend is sealed by a cover attached to the housing. This seal is ldiiiicult to maintain and therev Figure 1 is a. longitudinal section of a pump constructed according to the invention;

Figure 2 is' .a section on the line 2-2 of Figure 1;

Figure 3 is a section on the line 3-3 of Figure 1;

Figure 4 is an end view of a modified construction adapted to be supported entirely by the pipe line;

Figure 5 is a longitudinal section of another modification;

Figure 6 is a section on the line 6 6 of Figure 5, and

Figure 7 is a detail section of still another modication.

Reference to these views will now be made by use of like characters which are employed to designate corresponding parts throughout.

In Figures 1, 2 and 3, the pump is shown as built in a substantially cylindrical lhousing l having a base 2 with bolt holes 3 for attachment to a suitable support. At one end of a the housing is formed a cylindrical rotor chamber 4 in which is mounted a, rotor or internal gear 5. 'I'his member is formed with convex teeth 6 forming interdental spaces 1.

In the housing is journaled a shaft 8 eccentric of the gear 5 and extending into the same. The shaft is preferably enclosed partially in a sleeve 9 at one end of which. is an oil seal I0 engaged by a cover plate Il suitably attached to the housing. Within the gear 5, the shaft 3 carries a driving pinion I2 of the same length and meshing therewith. For this purpose, the pinion preferably has at least one tooth less `vthan! the gear 5. In meshing position, one of both parts were made of metal. For example, the' theoretical center distance for a running fit or mesh of metal parts is altered, with the result that there is a. compression of the resilient member rather than binding or breaking of the parts.

In'the construction shown, this alteration is eifected by reducing the theoretical center kdistance. Line A in Figure 2 is the center line of the internal gear 5, and line Bis the theoretical center line of the driving pinion I2 for a normal running flt. However, the theoretical center distance is reduced by displacing the actual center line of the driving pinion to position C, with the resultthat all but one of the pinion teeth I3, if not all the teeth, penetrate into the convex gear teeth e, as clearly illustrated in Figure 2. Ihe same result may be accomplished by making the driving -pinion slightly oversized in its theoretical relation to the gear 5.

Around the shaft 8, the housing I is formed with an intake chamber I5 and an exhaust chamber I 8, each extending nearly 180 around the shaft but separate from each other and communicating with the interior of the gear 5 at one end thereof. Tapped openings Il and I8 are formed from the outer surface of the pump housing i to the chambers I5 and I8 respectively for connection of the inlet and outlet lines. The end of the housing at which the rotor chamber l is formed is closed by a. cover plate I9 suitably secured to the housing, with a gasket 28 interposed.

In the operation of the pump, fluid admitted to the chamber I5 is delivered to the chamber I 6 by the rotation of the driving pinion I2 and gear 5 and their relative movement, according to principles well known in the art. -At the same time, as already indicated, the resilient member is compressed as it is traversed by the teeth of the hard member. The result is a positive and unfailing sealing action and self-priming, together with the other known advantages of perfect sealing, without the necessity of highly accurate machining and regardless of normal wear.

The spur teeth I 3 of the pinion I2 are preferably convex, with their side walls merging smoothly into the concave spaces I3. The elimination of sharp edges in this manner avoids mutilation of the resilient member as it moves relatively to the hard member.

At recurring intervals one of the spur teeth i3 takes a position symmetrical with respect to a common center line or planeD passing through both gears and between the intake and-'exhaust chambers. At such times the remaining spur teeth are symmetrically arranged with respect to the' common center line or plane, and the pressures acting to compress the resilient member are balanced. Not only does, this balancing of pressure contribute to smooth operation of the pump, but the pump can also be run in one direction as easily as in the other. The resilient member preferably contains a lubricant to facilitate its running in the rotor chamber l in case the rotor gear is resilient. In this connection it is understood that, within the scope of the invention, the driven member may be hard and the driving member resilient.

In the modification shown in Figure 4, the casing 2i is made cylindrical or symmetrical and without a base. This construction lends itself to being supported solely by the pipe lines 22 connected thereto. 'I'he interior of the pump is constructed inthe manner previously described.

In the modification shown in Figures 5 and 6, the housing is preferably built in two parts 25 and 26 for purposes of manufacture and assembly. The rotor chamber 21 is formed in the face of the part 25 and contains the rotor gear 28. The intake and exhaust chambers 29 and 30 respectively are formed in the part 28 and adjacent to the rotor chamber 21.

The drive shaft 3l]l is journaled in the part 28 in the manner previously described and carries the driving pinion 3| meshing with the rotor or internal gear 28. A similar intake chamber 28 is formed at the other side of the rotor chamber 21 in the part 25.

The inlet 32 is formed above one end of the intake chambers 28 and 29. Extending from the inlet, passages 32 are formed in the parts 25 and 28 and extend respectively to the chambers 29 and 29', but not to the exhaust chamber 38 as may be seen by a comparison of Figures 5 and 6.

The gear structure may be as described in connection with Figures 1 and 3, so that fluid is carried from the chambers 29, 29 to the exhaust chamber 30 and discharged from the latter through an outlet 33. Thus, the fluid is admitted into the rotor at both sides or faces thereof and discharged from only one side. Consequently the pump is constantly filled with fluid, if an adequate supply is available, regardless of how rapidly it may be operating.

The type of internal gear shown in Figure 1 has only one end in communication with the intake and exhaust chambers, and consequently the other end must be sealed in the housing. This condition presents a practical diiculty since leakage often appears at the plate I9 Figure 1.

This diiiiculty is overcome by the construction shown in Figure 7. The pump housing is con- `structed substantially as in Figure 1, with a cylindrical rotor chamber 36 formed therein from one end. Adjacent thereto are formed the intake chamber 37 and the exhaust chamber 38. 'I'he rotor or internal gear 39 mounted rotatably in the rotor chamber has one end communicating with the chambers 3l and 38 and the other end closed by an integral back wall 40. Finally, a cover plate 6I is laid across the back wall 40 and secured to thehousing 35 by suitable means. Thus, the internal gear is cup shaped rather than open on both ends and in communication with the charnbers 3'! and 38 only where flow occurs, with the result that the possibility of leakage is greatly reduced.

The housing 35 has a shaft 42 journaled therein for carrying the driving pinion :$3 cooperating with the internal gear 39 in the manner previously described.

For an operative and more detailed description of the operation of the pump, reference will again be made to Figure 2. The pinion I2' need not be oversized with reference to the gear 5. However, the spaces l are preferably narrower than the pinion teeth i3, so that there is no looseness of the teeth in the spacespursuant to the reduction of the center distance, as here illustrated and described above.y

In an actual construction, the diameter oi the bore or chamber 4 is 1.937 inches. The outside diameter of the annular gear is 1.900 to 1.905' inches. This leaves normally a clearance for the annular gear in the chamber. 1

The internal diameter of the annular gear, from the bottom of a space 1 to the crown of the opposite tooth 6, is 1.1875 inches. This is also the'outside or maximum diameter of the pinion i2. y Y

Before the pinion is inserted in the annular gear, there is a clearance of .0185 to .0.16 inch running t of the same members in metal,A said driven member having convex teeth and having interdental spaces, said driving member having between the annular gear and the chamber wall.

After the pinion has been'inserted, at its reduced center distance, the clearance around the annular gear is about .005 inch. In other words, the

pressure of the pinion teeth against the annular gear is translated into a circumferential stretch of the latter without 4actually contacting the chamber wall. This stretch is a limit under the conditions described, `whereby the pinion teeth may engage 'the annular gear 'under pressure without forcing the gear into actual contact with the chamber wall. This condition exists, leaving a running 4clearance around the annular gear, when the center distanceis reduced .110 inch from the normal or theoretical value with the dimensions given herein. It will be understood that this is merely one example of an actual pump construction andis not a limitation on the scope of the invention, vsince obviously these relations may be obtained in various other sizes of pumps.

What I claim ist spur teeth receivable in said spaces and having concave interdental faces positioned and dimensioned to coincide successively with said convex teeth in the meshing of said members, whereby the resilient member is compressed by the other member as .the spur teeth move across said convex teeth. Y

2. A pump comprising a housing having an inlet and an outlet, a rotatably mounted outer driven member therein in the form of an internal gear, a driving gear member rotatably mounted eccentrically within said driven member and having one tooth less than said driven member, said driven member having substantially the resiliency of rubber, the distance between centersV of said Y members being less than required for a running nt `of the same members in metal, said driven member having convex teeth and having interdental spaces, said driving member having spurl teeth receivable in said spaces and having concave interdental faces positioned and dimensioned to coincide successively with said convex teeth in the meshing of said members, whereby the resilient member iscompressed by the other member as the spur teeth move across said convex teeth.

MICHAEL SCHMITZ. 

